1. Field of the Invention
The present invention relates to information recording media which comprise a high density information recording means such as an optical information recording medium including an optical disk or a magnetic information recording medium including a fixed magnetic disk or a floppy disk, a tracking error signal detection apparatus for the information recording media, and an information recording apparatus which can precisely record, reproduce and erase information on the information recording media using the tracking error signal detection apparatus, and also relates to methods of adjusting an information recording apparatus.
2. Disclosure of the Prior Art
A track pitch of a conventional magnetic recording media on which information is recorded, such as a floppy disk. Therefore, the track pitch is much wider than that of an optical disk, which is about 1.6 xcexcm. Accordingly, a rough track location using a mechanical method such as a stepping motor has been sufficient. However, in order to realize a magnetic recording medium having a larger capacity, a track pitch from several xcexcm to several tens xcexcm m is required. In this case, a precise track location becomes necessary.
FIG. 1 shows a configuration of a conventional magnetic recording apparatus which detects a tracking error signal by using light. In FIG. 1, a linearly polarized divergent beam 70 radiated from a semiconductor laser light source 10 is converted to a parallel beam by a collimator 20 and the parallel. beam enters a polarizing beam splitter 30. All the parallel beam 70 entering the polarizing beam splitter 30 passes through the polarizing beam splitter 30 and enters a xc2xc wavelength plate 31. The parallel beam 70 is converted to a circularly polarized beam by passing through the xc2xc wavelength plate 31 and is focused on a magnetic recording medium 40 by an object lens 21.
FIG. 2 shows the relationship between the magnetic recording medium 40 and the focused light beam 70. The magnetic recording medium 40 has tracks Tnxe2x88x921, Tn, Tn+1 . . . , which include the area on which information is recorded or reproduced by a magnetic head 99 with a certain pitch pt (approximately 20 xcexcm). Further, discrete guiding grooves Gnxe2x88x921, Gn, Gn+1 . . . , which enable the optical detection of a signal synchronizing A tracking error signal and which enables rotations of the magnetic recording medium 40, are formed in the middle of adjacent tracks.
The beam 70 reflected and diffracted by the magnetic. recording medium 40 passes through the object lens 21 again, and enters the xc2xc wavelength plate 31. By passing through the xc2xc wavelength plate 31 again, the beam 70 is converted to a linearly polarized beam having a 90xc2x0 phase change of the light source 10. All the beam passing through the xc2xc wavelength plate 31 is reflected by the polarizing beam splitter 30 and enters a photodetector 50. The incident light beam is converted into an electric signal by the photodetector 50 and inputted to a signal processing portion 80.
As illustrated in FIG. 1, the photodetector 50 has two light sensing portions 501, 502. Signals outputted from the light sensing portions 501, 502 are converted to voltage signals by current-voltage (I-V) converting portions 851, 852 respectively, and inputted to a differential operation part 871. The differential operation part 871 subtracts the two voltage signals outputted from the I-V converting portions 851, 852.
When a beam 70 from the optical system has a displacement x from the center of a guiding groove such as Gn on a magnetic recording medium 40, voltage signals v21, v22 outputted from the I-V converting portions 851, 852 become sine waves having opposite phases which can be approximately represented by the below mentioned formulae (1) and (2). The signals v21, v22 can be illustrated as FIG. 3(a) and (b).                     v21        =                                                            -                A                            ·              sin                        ⁢                          xe2x80x83                        ⁢                          (                              2                ⁢                                  xe2x80x83                                ⁢                π                ⁢                                  xe2x80x83                                ⁢                                  x                  /                  pt                                            )                                +          B                                    (        1        )                                v22        =                                            A              ·              sin                        ⁢                          xe2x80x83                        ⁢                          (                              2                ⁢                                  xe2x80x83                                ⁢                π                ⁢                                  xe2x80x83                                ⁢                                  x                  /                  pt                                            )                                +          B                                    (        2        )            
In the formulae (1) and (2), A is an amplitude and B is a DC component.
A signal v23 outputted from the I-V converting portion 871 can be represented by the below mentioned formula (3) and outputted from a terminal 801 as the tracking error signal.
v23=2xc2x7Axc2x7sin(2xcfx80x/pt)xe2x80x83xe2x80x83(3)
The signal v23 can be illustrated as FIG. 3(c). The tracking error signal v23 outputted from the terminal 801 is inputted to a driving portion 90 to adjust relative positions of a magnetic recording medium 40 and a base 95 including a tracking error signal detection optical system 100 and a magnetic head 99 for recording and reproducing information so as to form a desired track on the magnetic recording medium 40. The tracking error signal detection method is known as the push pull method.
(First Problem)
In a conventional magnetic recording apparatus using a magnetic head 99 for recording and reproducing information, and an optical system 100 for the detection of a tracking error signal, a distance d between a point S1 at which the magnetic head 99 contacts a magnetic recording medium 40 and a focal point S2 of a beam 70 from the optical system needs to be at least several hundred xcexcm to several mm. That is, the point S1 at which the magnetic head 99 contacts the magnetic recording medium 40 and the focal point S2 of the beam 70 scan different tracks on the magnetic recording medium 40.
In assembling a magnetic recording apparatus, the distance d is adjusted so as to have the working point of the tracking servo at the midpoint S3 of the signal amplitude of the tracking error signal v23 as illustrated in FIG. 3(c) when the point S1 is on a track of the magnetic recording medium 40. However, temperature or humidity change causes expansion or contraction of the magnetic recording medium 40 and the track pitch pt changes accordingly. Therefore, in the tracking operation at the point S3 using the tracking error signal v23 obtained from the optical system 100, the point S1 becomes off track and thereby drastically deteriorates the information reproduction characteristics.
In this case, for example, if a point S4 is the working point on the tracking error signal when the point S1 is on the track, a tracking servo can be enabled by applying an offset voltage to the tracking servo. However, the dynamic range of the orientation illustrated by the arrow D1 lowers and thereby deteriorate the followability in the case disturbance generates. Further, as the point S4 moves farther from the point S3, the servo gain of the tracking operation lowers. When the point S4 eventually reaches the point S5, a new problem occurs that the servo gain of the tracking becomes 0 thereby completely losing the tracking servo.
On the other hand, in an optical disk apparatus where the beam used to detect tracking error signals and the beam used to record information on the information recording medium are identical, a configuration forming a track on or between the guiding grooves so as to record and reproduce information with a further high density is proposed. However, in this configuration, when the relationship pt greater than xcex/NA is satisfied where xcex is a wavelength of the beam radiated from the light source, NA is an numerical aperture of the object lens at the information recording medium side, and pt is a cycle of marks or guiding grooves formed on the information recording medium to enable the detection of the tracking error signals, a problem similar to the above mentioned problem occurs when the predetermined angle between the beam focused by the object lens and the information recording medium can not be sustained.
Specific examples include the case having a wavelength xcex of 650 nm, a numerical aperture NA of 0.6, a cycle pt of marks or guiding grooves of 1.48 xcexcm, and a substrate thickness for the information recording medium of 0.6 mm.
(Second Problem)
Dusts or flaws on the magnetic recording medium 40 change the reflection ratio of the magnetic recording medium 40 and the intensity of a light beam 70 reflected thereby accordingly. In this case, a problem occurs in that an offset occurs in the tracking error signal, and thus the magnetic head 99 can not be controlled on a desired track of the magnetic recording medium 99.
(Third Problem)
Moreover, as in the above mentioned prior art, if a stepping motor is used in the tracking driving portion 90 for a magnetic recording medium having a track pitch of several xcexcm to several tens xcexcm for seeking tracking error signals using a light beam, an off track generates which depends on the step width of the stepping motor. By making the step width narrower to reduce the off track amount, a problem occurs in that the time for detecting tracks becomes longer. These two problems can be solved by the use of a DC motor instead of a stepping motor in the tracking driving system. However, since mechanical positioning can not be controlled if a DC motor is employed in a tracking driving portion 90, a new problem occurs in that information can not be recorded or reproduced in a magnetic recording medium having a track pitch of 188 xcexcm, which is now widely used.
(Fourth Problem)
Further, an optically optimum value for a numerical aperture NA of the object lens 21 for a magnetic recording medium having a track pitch of 50 xcexcm is about 0.017. However, when an angular dislocation xcex8 exists between the beam 70 focused by the object lens 21 and the magnetic recording medium 40, the beam 70 reflected by the magnetic recording medium 40 can not enter the aperture. Therefore a problem occurs in that the quantity of the light beam introduced to the photodetector 50 decreases and thus the tracking operation becomes unstable. The relationship between a performance function Ev with respect to the angular dislocation xcex8 (Ev=0.5xc2x7tan(2xc2x7xcex8)/NA) and a quantity of light I of the beam 70 introduced by the photodetector 50 is shown in FIG. 4. With a numerical aperture NA for the object lens 21 of 0.017, the angular dislocation xcex8 is 0.97 when the quantity of light I of the beam 70 on the photodetector 50 is 0, namely, the performance function Ev is 1. In this case, the tracking error signal can not be obtained at all.
A first object of the present invention is to provide a tracking error signal detection apparatus which can realize a tracking servo operation with a constant stability without deteriorating the dynamic range or the gain of the tracking error signal.
That is, a first tracking error signal detection apparatus of the present invention comprises a light source to radiate a light beam, a converging optical system to converge the light beam radiated from the light source on a reflecting body in a minute spot, a beam splitting means to split the light beam reflected and diffracted by the reflecting body, a photodetector to sense the beam splitted by the beam splitting means and output a signal according to the quantity of light, a first arithmetic means to process a signal outputted from the photodetector, a changeable gain amplifying means to change the intensity of the signal outputted from the arithmetic means and output at least two signals, and a second arithmetic means to add or subtract the two signals outputted from the changeable gain amplifying means.
In the above mentioned configuration, the movement of the working point in the tracking error signal can be detected as the phase change of the signal outputted from the second arithmetic means by processing the two signals outputted from the changeable gain amplifying means by the second arithmetic means. In this case, by sustaining the amplitude of the tracking error signal at a certain level and operating the tracking servo operation at the middle of the amplitude of the tracking error signal, the magnetic head can be positioned properly on the track.
A second object of the present invention is to provide a tracking error signal detection apparatus which is not liable to generate the offset in the tracking error signal even when a reflection ratio of the information recording medium changes partially.
That is, a second tracking error signal detection apparatus of the present invention comprises a light source to radiate a light beam, a converging optical system to converge the light beam radiated from the light source on a reflecting body in a minute spot, a beam splitting means to split the light beam reflected and diffracted by the reflecting body, a photodetector to sense the beam splitted by the beam splitting means and output a signal according to the quantity of light, and a signal processing portion to process the signal outputted from the photodetector to generate a tracking error signal, wherein a cyclic physical change which changes the reflecting ratio is formed on the reflecting body so as to have a magnitude of a light beam in the orientation parallel to the physical change larger than the magnitude of the light beam in the orientation orthogonal to the physical change.
In the above mentioned configuration, the change of the beam intensity depending on the partial reflecting ratio change of the reflecting body can be reduced by enlarging the magnitude of the beam focused on the reflecting body. Thus a tracking error signal having little offset can be detected.
A third object of the present invention is to provide a magnetic recording apparatus which can detect a tracking error signal on either a magnetic recording medium having a track pitch of several xcexcm to several tens xcexcm or a magnetic recording medium having a track pitch of 188 xcexcm.
In order for the third object, a first magnetic recording apparatus of the present invention comprises a light source to radiate a light beam, a first converging optical system to converge the light beam radiated from the light source on a first reflecting body in a minute spot, a second converging optical system to converge the light beam radiated from the light source on a second reflecting body in a minute spot, a beam splitting means to split the light beams reflected and diffracted by the first and second reflecting bodies, an photodetector to sense the beams splitted by the beam splitting means and output signals according to the quantity of light, a magnetic head to record information on the information recording medium or to reproduce information on the information recording medium, a signal processing portion to generate a tracking error signal from a plurality of signals outputted from the photodetector, and a control means to control the tracking of the magnetic head with respect to the information recording medium based on the tracking error signal, wherein a cyclic physical change is formed on the first and second reflecting bodies, and the cycle of the physical change formed on the first reflecting body and the cycle of the physical change formed on the second reflecting body are different.
In the above mentioned configuration, since a tracking error signal can be generated using a light beam reflected by the first reflecting body for a magnetic recording medium having a track pitch of several xcexcm to several tens xcexcm, and a tracking error signal can be generated using a light beam reflected by the second reflecting body for a magnetic recording medium having a track pitch of a 188 xcexcm, a tracking operation can be conducted on magnetic recording media having different tracking pitches.
A fourth object of the present invention is to provide a magnetic recording apparatus which can detect a tracking error signal stably even when an angle dislocation xcex8 exists between the beam 70 focused by the object lens 21 and the magnetic recording medium 40, and an adjusting method thereof.
That is, a second magnetic recording apparatus of the present invention comprises a light source to radiate a light beam, a converging optical system to converge the light beam radiated from the light source on a reflecting body in a minute spot, a beam splitting means to split the light beam reflected and diffracted by the reflecting body, an photodetector to sense the beam splitted by the beam splitting means and output a signal according to the quantity of light, and a magnetic head to record information on the information recording medium or to reproduce information on the information recording medium, wherein a cyclic physical change which changes the reflecting ratio is formed on the reflecting body and further comprises any of the belong mentioned components (1) to (3):
(1) two mirrors formed integrally on a common supporting body to change the orientation of a beam on the optical path extending from the light source to the reflecting body,
(2) a converging optical system having an aperture in the second orientation larger than an aperture in the first orientation with the premise that the orientation of the cyclic physical change of the reflecting body is the first orientation and the orientation orthogonal to the first orientation is the second orientation, and
(3) a converging optical system having a diffraction element formed in the vicinity thereof.
An adjusting method in assembling a magnetic recording apparatus of the present invention wherein the magnetic recording apparatus comprises a light source to radiate a light beam, a converging optical system to converge a light beam radiated from the light source on a reflecting body in a minute spot, a beam splitting means to split the light beam reflected and diffracted by the reflecting body, a photodetector to sense the beam splitted by the beam splitting means and output a signal according to the quantity of light, and a magnetic head to record information on the information recording medium or to reproduce information on the information recording medium, wherein the light source is located in a position orthogonal to the optical axis of the converging optical system so as to have a predetermined angle formed by the beam focused by the converging optical system and the reflecting body.
By having the component (1), an angle dislocation between the optical axis of the beam focused by the converging optical system and the magnetic recording medium caused by the installation error of the mirror used for reducing the area occupied by the optical system can be prevented since the movement of a mirror can be offset by the movement of another mirror.
By having the component (2), since an numerical aperture NA in the second orientation becomes larger, the effect of the vignetting of the light beam in the converging optical system caused by an angle dislocation between the optical axis of the beam focused by the converging optical system and the magnetic recording medium can be avoided.
By having the component (3), since a light beam in the converging optical system which moves depending on an angle dislocation between the optical axis of the beam focused by the converging optical system and the magnetic recording medium can be guided to an sensing element by the diffraction element, a vignetting of the light beam in the converging optical system can be prevented.
Accordingly, in any case, a magnetic recording apparatus which can stably detect a tracking error signal stablly can be provided.
Moreover, since an angle dislocation between the optical path of the light beam focused by the converging optical system and the magnetic recording medium caused by the installation error of elements comprising the magnetic recording apparatus can be compensated in the above mentioned adjusting method, a light beam reflected by the reflecting body can always return to enter the aperture of the lens, and thus a tracking error signal can be detected stably.